Need Help Jobless Run

So, I'm near the end of my jobless run. This run involves not using any of the job classes ever and trying to keep levels as low as possible. I want to get the Ragnarok and Dragon Beard from Shinyruu before going to fight Exdeath.

My setup is Hermes Sandals and Mirage Vests on all characters. I'm able to berserk Shinyruu with Power Staff before he does anything, so the normal equipment that people usually use is not needed. One character has my thief equipment and the others have best weapons available Brave Blade, Apollos Harp.

Any suggestions on how I can win this fight? Thanks.